01.<html>
02.<head>
03.<title>ThaiCreate.Com Tutorial</title>
04.</head>
05.<body>
06.<form name="frmMain" action="" method="post">
07.<script language="JavaScript">
08. function fncSum()
09. {
10. if(isNaN(document.frmMain.txtNumberA.value) || document.frmMain.txtNumberA.value == "")
11. {
12. alert('(Number A)Please input Number only.');
13. document.frmMain.txtNumberA.focus();
14. return;
15. }
16.
17. if(isNaN(document.frmMain.txtNumberB.value) || document.frmMain.txtNumberB.value == "")
18. {
19. alert('(Number B)Please input Number only.');
20. document.frmMain.txtNumberB.focus();
21. return;
22. }
23.
24. document.frmMain.txtNumberC.value = parseFloat(document.frmMain.txtNumberA.value) + parseFloat(document.frmMain.txtNumberB.value);
25. }
26.</script>
27.Number A <input type="text" name="txtNumberA" value=""> <br>
28.Number B <input type="text" name="txtNumberB" value=""> <br>
29.A + B = <input type="text" name="txtNumberC" value=""><br>
30.<input type="button" name="btnSum" value="Sum" OnClick="fncSum();">
31.</form>
32.</body>
33.</html>
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